8 Vectors intro


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8 Vectors intro

  1. 1. Dr. Nik Ahmad Irwan Izzauddin Nik Him Room 4o3, nikirwan@usm.my 1
  2. 2.  Introduction and important aspects of vectors in disease transmission – important concepts, terms and definitions Arthropod vectors – Mosquitoes as disease vectors-its role as important human disease vector for dengue, microfilaria and malaria 2
  3. 3. Introduction and important aspects of vectors in disease transmission – important concepts, terms and definitions 3
  4. 4.  The most successful animal group Arthropods have huge impact on health of humans & domestic animals  Irritation & diseases Relatively few species involved but serious social & economic consequences Leishmaniasis  Transmit diseases (vectors)  Inject venoms & transmit allergens  Cause wounds Myiasis  Create nuisance & phobias Other arthropod groups also very important 4
  5. 5.  Major insect orders  Diptera (flies)  Hemiptera (true bugs)  Phthiraptera (lice)  Siphonaptera (fleas) Diseases & causative pathogens Other arthropod groups  Acari (ticks & mites)  Araneae (spiders) Protozoan causing  Scorpiones (scorpions) sleeping sickness 5
  6. 6.  Nuisance mostly related to high densities & not real hazards  Justified in case of biting, venomous & filth-frequenting species Major causes of nuisance & irritation  Blood-feeding species  Lachrymal-feeders  Immunological reactions  Phobic responses (delusory parasitosis) Large industries are focused on pest control Mosquito feeding frenzy 6
  7. 7.  Vector - Definition: Organism that are capable of transmitting other organisms that cause disease in vertebrate host Carrier, bearer In parasitology  An organism or vehicle that transmits the causative agent or disease-causing organism from reservoir to the host 7
  8. 8.  Vectors generally don’t become “ill” from carrying their various viral, protozoan and nematode infections. They might accrue some damage to their tissues, but in some cases this “damage” actually makes them more likely to transmit and infect. A mosquito with problems in its feeding apparatus will need to take additional bites to complete a blood meal. A flea with a gut clogged with plague bacteria will regurgitate more. 8
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  11. 11.  Primary vector - If they are proved to be transmitting a pathogen to man or other animal Secondary vector - If they play a supplementary role in transmission, but would be unable to maintain a disease in the absence of primary vector 11
  12. 12. Case sample:In the transmission of dengue fever in Malaysia Aedes egypti is the main vector… and Aedes albopictus is the secondary vector 12
  13. 13.  In instances where a disease of unknown cause is occurring, certain general characteristics help to identify its vector Establishment of the relationship of arthropod populations to transmission of a particular disease agent is called vector incrimination The process of knowing which species of arthropod is serving as a vector of a particular disease 13
  14. 14. • There are 4 major criteria for incriminatingarthropods as vectors of human diseaseBarnett, H. C. 1956. The transmission of western equine encephalitis virusby the mosquito Culex tarsalis Coq. Am. J. Trop. Med. Hyg. 5: 86-98. 14
  15. 15.  Identifying contact between arthropod and host - suck blood for meal  YES Having a biological association in time - the rate of cases higher in correlation to the higher number of Aedes  YES Repeated demonstration of disease between arthropod and host - The infective stage have been found consistently in Aedes and they transferred it during feeding  YES Replicable under experimental conditions - Can be rearing in the lab and the and can be replicated  YES 15
  16. 16.  The time that elapses between the invasion of a susceptible host by an infectious agent and the onset of symptoms of the disease caused by that agent is called the incubation period The length of the incubation period varies greatly Extrinsic Incubation period – a period in a vector during which the disease-producing organism/parasite increases or transforms to a point where it can be transmitted. Intrinsic incubation period – a period in the vertebrate host before disease is expressed clinically 16
  17. 17. Case sample: MalariaExtrinsic incubation period Intrinsic incubation period17
  18. 18.  Vectorial capacity describes the potential of agroup of arthropods to transmit a given pathogen Vector effectiveness There are 6 main determinants: – Abundance – Host preference and host-feeding patterns – Reproductive capacity – Longevity – Dispersal – Vector competence 18
  19. 19.  The more vectors there are, the higher the probability of disease transmission because it has a direct bearing on the probability of vector-host contact 19
  20. 20.  Knowing what the vectors feed upon allows for identification of disease transmission Patterns of host feeding that are determined by identification of blood meals in vectors are usually the end result of many factors, including host preference and host availability. 20
  21. 21.  A measure of the rate at which a population of vectors increases Fecundity is a related term which relates to the number of generations, broods, or litters produced per unit of time. The net reproductive rate of a population of vectors is a combination of fecundity and survival. Survival is influenced by various mortality factors, including predation and diseases, as well as accidents and natural aging 21
  22. 22.  Longevity is knowing how long the stages of the vector’s life cycle last A vector must feed more than once to transmit pathogens It is essential that a vector live a sufficient period of time Maximal longevity will permits vectors to serve as essential parts of the reservoir of infection. 22
  23. 23.  Dispersal is knowing how far a vector can fly or move about freely – The greater the movement, the greater chance for spread of disease Vectors that can move freely and for long distances will have greater chances for contact with humans, and will be more likely to move between infected and noninfected hosts. Superior mobility aids in the dissemination of pathogens over a wide area, so that their associated diseases are not limited or focal in nature. Flying vectors (e.g. mosquitoes, flies) generally make a good vector; however crawling vectors (e.g. fleas, lice, mites and ticks) are distributed by the relative mobility of their hosts. 23
  24. 24.  The susceptibility of a group of arthropods to a given strain of pathogen and the ability of those arthropods to transmit the pathogen These traits are under genetic control, and although infection and transmission in vectors will vary with temperature, vector competence is considered to be an innate characteristic for a particular vector for a given microorganism 24
  25. 25.  Mechanical transmission Biological transmission - Cyclodevelopment transmission - Propagative transmission - Cyclopropagative transmission 25
  26. 26.  This is when the pathogen adheres to body hairs, spines, sticky pads, or other structures of insects – In the case of certain insects, transmission may be by regurgitation or defecation - Biting flies may transmit pathogens by biting with contaminated mouthparts Nearly all mechanically transmitted diseases can also be transmitted in other ways (e.g., contaminated food and water) e.g. houseflies, cockroaches 26
  27. 27.  The parasites undergo several molts in the body of the vector No multiplication takes place within the body of the vector The only pathogens that are transmitted this way are filarial nematodes - Start out as a microfilariae and develops into an infectious larvae Also known as Cyclical transmission 27
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  29. 29.  In this type of transmission, the pathogen multiplies within the body of the vector, but does not undergo any changes in form Most viral diseases fall into this category Plague (a bacterial disease) is also an example Any stage of these pathogens can infect a vertebrate host 29
  30. 30.  Both multiplication and changes in the life form of the pathogen occur within the vector Examples are malaria, leishmaniasis, both caused by protozoan parasites Also known as Propagative and Cyclical transmission 30
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  32. 32.  Horizontal and vertical transmission describe the pathway a pathogen takes among vectors and hosts. Horizontal transmission - Horizontal transmission involves the pathogen being transmitted by a vector to a host in a cyclical pathway Ventricle transmission - Vertical transmission is more direct and does not involve a host, but occurs directly from infected mother/female to offspring – This is also called transovarial transmission 32
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  34. 34.  Dead end host – a vertebrate that harbors the pathogen and is severely affected by it, yet the level of pathogen in its body is too low for blood sucking vector to become infective after feeding on the host. Amplifying host – a vertebrate that has high level of pathogen that a feeding vector will likely become infectious. Silent host – one that harbors the pathogen, but shows no obvious signs of disease. 34
  35. 35.  Resistant host – one that is not naturally affected by a pathogen. Partially resistant host – one that harbors the pathogens for a long period before being overcome by it. Susceptible host – a victim of the pathogen 35
  36. 36.  Reservoir refer to any vector or host, capable of maintaining a pathogen for considerable periods of time. Usually, they show no evidence of serious disease, or a reservoir of infection may be maintained by continuous transmission among a group of severely affected animals. Most vectors are short-lived and would not serve as important components of reservoirs, except possibly through aestivation or hibernation. 36
  37. 37.  At the end of the nineteenth century, it was discovered that certain species of insects, other arthropods and freshwater snails were responsible for the transmission of some important diseases. The discovery of the insecticide dichlorodiphenyltrichloroethane (DDT) in the 1940s was a major breakthrough in the control of vector- borne diseases. In 1950s and early 1960s --> -To eradicate the diseases or to reduce transmission to such low level that control could be maintained through the general health care facilities without the need of control measures. Problem  resistance  expensive 37
  38. 38.  Vector control methods suitable for community involvement should:— be effective;— be affordable;— use equipment and materials that can be obtained locally;— be simple to understand and apply;— be acceptable and compatible with local customs, attitudes and beliefs;— be safe to the user and the environment. 38
  39. 39.  Before starting any vector control activity, it is important to ask two questions: What result do you want to achieve: merely to protect yourself or your family from biting pests and the diseases they carry, or to reduce disease in the community? Are the health authorities already carrying out control measures and do you want to provide the community or your family with additional protection from disease? 39
  40. 40.  Important factors to take into consideration - Biological factors - Availability of technical tools - Socio-economic considerations 40
  41. 41.  Species affected Density of susceptible species Wildlife reservoir Vector transmission Transmissibility Current extent of disease Survival in the environment Carrier state Ease of clinical recognition 41
  42. 42.  Diagnostic tests Vaccines Treatment Effectiveness of isolation/ quarantine Disinfection 42
  43. 43.  Cost and benefits of intervention Ease of implementation Stake holder engagement Political will 43
  44. 44.  2 control methods1. Self-protection2. Community control 44
  45. 45.  Self-protection measures are used to protect yourself, your family or a small group of people living or working together from insect pests or vectors of disease. These measures include personal protection,1. the prevention of contact between the human body and the disease vector,2. and environmental measures to prevent pests and vectors from entering, finding shelter in, or breeding in or around your house. These measures are usually simple and inexpensive, and can often be adopted without help from specialized health workers. 45
  46. 46.  Example: Repellents Protective clothing Insecticide vaporizers Mosquito nets Insecticides - Insecticide spraying of walls - Space-spraying with insecticides - Treating fabrics with an insecticide Anti-mosquito screening Prevention of breeding - Source reduction - Biological control - Larvicides - Insect growth regulator 46
  47. 47.  The type of control may be the same as for the protection of an individual or a family, but is, of course, larger. Before investing resources in community-wide control efforts, advice should be obtained from health workers on the type of measures most likely to be successful under local conditions. Before investing resources in community-wide control efforts, advice should be obtained from health workers on the type of measures most likely to be successful under local conditions. 47
  48. 48.  Many factors need to be taken into account:1. the vector species and its behaviour,2. the compatibility of control methods with the local culture,3. affordability in the long term, the need for expert advice 48
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